The present invention relates to a variable power optical system for shooting an object, and to an imaging apparatus having the variable power optical system.
Recently, imaging apparatuses having a zooming function (e.g., digital cameras, digital video cameras and digital electronic devices in which an imaging module mounted) have become widespread. Incidentally, such digital electronic devices include a mobile phone, a PDA (Personal Digital Assistant), a PND (Portable Navigation Device), a PHS (Personal Handy phone System), a portable game machine and a notebook computer. In order to increase the degree of freedom in regard to portability and design of such cameras and digital electronic device, it is desirable that the variable power optical system mounted on an imaging apparatus is designed to be thin and compact in size.
Japanese Patent Publication No. 3709148B (hereafter, referred to as patent document #1) describes a variable power optical system of a retractable type including a negative lens group, a positive lens group and a positive lens group, i.e., three lens groups. The variable power optical system described in patent document #1 is configured such that all the lens groups are aligned along an axis. Therefore, it is difficult to reduce the size in the thickness direction of an apparatus. Hence, the variable power optical system is unsuitable for design for reducing the thickness of an apparatus.
Japanese Patent Provisional Publication No. 2007-052273A (hereafter, referred to as patent document #2) describes a variable power optical system configured such that an optical path is bent by arranging a right angle prism in a first lens group. The variable power optical system described in patent document #2 is a so-called bending optical system configured to bend an optical path so that the thickness of an apparatus can be reduced. Immediately after the right angle prism, a negative lens group which moves during focusing is arranged. The interval between the right angle prism and the negative lens group is designed to be relatively wide in consideration of a moving amount of a lens during near distance shooting and a clearance to avoid mechanical interference. However, as the interval between an exit surface of the right angle prism and the negative lens group increases, a height from the optical axis defined in the right angle prism with respect to a light ray proceeding to a peripheral part of an image during long distance shooting increases. Therefore, it is necessary to employ a right angle prism having a large size, which is unsuitable for design for reducing the thickness of an apparatus.
Japanese Patent Publication No. 4191501B (hereafter, referred to as patent document #3) describes a variable power optical system configured such that a second right angle prism is additionally arranged immediately before an image pickup chip. Since the variable power optical system described in patent document #3 is configured to bend an optical path at two points, i.e., a point immediately after an entrance position of light and a point immediately before an exit position of light, it appears that the variable power optical system is suitable for reducing the thickness and size of an apparatus. However, patent document #3 merely describes a general configuration of the variable power optical system. That is, no explanation is made in patent document #3 about a concrete configuration of the variable power optical system for reducing the thickness and the size of an apparatus.